The present invention relates to a control circuit for driving and activating a plurality of electrical loads, especially electroluminescent loads such as electroluminescent fibers. More particularly, the present invention relates to a control circuit for sequentially driving such loads, one at a time (or one subset at a time), using the same power supply.
Lighting controllers (e.g., lighting consoles or boards) are commonly found in theatrical, architectural, and entertainment venues. These controllers are operated by an individual and/or a computer system to activate and control relays, switches, dimmers, illuminators, and other control devices that are integrated within a lighting system. Those control devices are in turn connected to lighting devices (and possibly other devices such as mirrors, gobo wheels, and smoke machines) to operate or enable the lighting devices in a desired manner. In most lighting systems, controllers activate and interface with control devices using the Digital Multiplex (DMX) protocol. The DMX (or DMX-512) protocol is a digital control signal standard published by the United States Institute for Theatre Technology (USITT) and is used extensively within the lighting industry (a corresponding Analog Mulitplex, AMX or AMX-192, protocol also exists). A DMX signal can be used to control timed events, color changes, scene changes, and numerous other effects.
The current DMX control standard (established in 1986 and revised in 1990) provides up to 512 control channels per data link. Each device needs a certain number of DMX channels for proper operation. Some control devices require only one or two channels, while others may use 20 or more channels with separate channels controlling different effects such as activation, dimming, color, strobing, tilting, and rotation. Each control device in a lighting system is assigned a DMX start channel or address number (if a device uses several channels, those channels are addressed sequentially beginning at the start address). DMX channel assignment is typically achieved by setting a DIP (dual in-line package) switch on each control device. Once channels have been assigned, the devices are typically connected in a serial or daisy-chain configuration, in which the controller connects to an input of a first control device, an output of the first control device connects to an input of a second control device, and so on.
A DMX control signal provides data in an asynchronous serial format at 250 kbps via the industry standard RS-485 interface (also known as EIA-485). A typical DMX data packet includes a reset condition, followed by a start code and up to 512 bytes of control data, with one data byte for each channel. The start code is usually a xe2x80x9c0xe2x80x9d byte, however, a unique start code can also be used to indicate to a receiving device that a data packet containing proprietary information is being sent. Each channel byte in a packet provides information for controlling the corresponding device or device feature. Although the DMX standard was originally designed to carry dimmer information (i.e., information directly affecting the proportional output from a stage lighting dimmer), DMX control data has since evolved to carry information for moving lights, color changers, and a variety of other devices used within entertainment and architectural lighting industries. Typically, by programming or sliding a potentiometer on a control console, a control output can be varied from 0-100% (with 8-bit resolution).
The data packets in a DMX signal are transmitted continuously, optionally with no delay between packets. As a result, the fewer channels used, the higher the possible refresh rate in the DMX control signal. Generally, the number of channels used in a given lighting system will vary according to the needs of the lighting system, however many lighting controllers use only a fraction of all available DMX channels. A more thorough description of the DMX-512 protocol is provided by John Huntington in Control Systems for Live Entertainment, Focal Press (1994), relevant portions of which are incorporated herein by virtue of this reference.
DMX control channels are generally assigned on a one-to-one basis corresponding to the various outputs (devices or features) that need to be controlled. Power is routed to the dimming or switching control devices and then internally distributed to multiple outputs. Conventional DMX control devices used in the lighting industry can control from one to many thousands of outputs, either one at a time or in any combination of multiple outputs. As a result, these devices are capable of providing considerable design versatility and flexibility, especially in controlling a number of lighting devices simultaneously. However, conventional DMX control systems may be wasteful and inefficient for certain lighting applications. In particular, in many lighting systems it is often desirable to activate a large number of loads (such as electroluminescent fibers), one at a time (or one subset at a time), in a desired sequence or order. When such sequencing applications are performed using conventional DMX lighting control, a separate relay (or other control device) and separate power supply are generally used to activate and energize each lighting device or load. Consequently, at any one time during the sequencing, all but one of the power supplies is idle and unused, resulting in significant technical and economic inefficiencies.
Sequencing control systems for driving a plurality of loads using a single power supply have been developed. For example, Weiner et al. in U.S. Pat. No. 4,215,277 describe a controller for sequentially energizing a plurality of light strings, each connected to an outlet receptacle via a triac switching device. A timing and logic circuit connects to a gating circuit for each triac switching device to provide selective energization of the triac and the corresponding light means connected to that triac. Similarly, Williams in U.S. Pat. No. 4,410,794 discloses a switching system for sequentially connecting an alternating current supply to a plurality of loads, in particular heater loads in an aircraft de-icing system. The system includes a computer for generating switch selection data, in the form of serial bits, to a distributor arrangement that decodes the selection data and provides control signals to switch devices that connect the loads to the supply. The distributor arrangement includes a circuit for inhibiting the supply of control signals to the respective switch devices unless the voltage of the supply phase connected by the device is substantially zero. The control signals are also time-advanced with respect to the zero voltage condition so that the switch devices can be placed in states in which they can connect a load prior to disconnection of a preceding load.
However, such prior art sequencing control systems are generally not compatible for operation with a DMX controller. This is disadvantageous sincexe2x80x94given the wide spread adoption of the DMX protocol in the lighting industryxe2x80x94lighting designers, stage hands, theater electricians, architectural lighting consultants, and special effects designers are accustomed to programming DMX controllers and are familiar with the usage, distribution and maintenance of DMX systems. Compatibly with the DMX protocol also conveniently allows the same control signal used to effect the sequencing operation to also operate and activate other devices in a lighting system that are unrelated to the lighting devices being sequentially switched.
In addition, the intensity and color of electroluminescent loads, such as electroluminescent fibers, may be varied based on the voltage and frequency, respectively, of the power supply signal. For example, it may be desirable for the power supply signal to vary between 90-150 VAC and 400-2500 Hz to adequately exploit the potential for intensity and color variation in a fiber. However, the above described prior art sequencing control systems are generally unsuitable for efficiently switching between lighting devices that may be powered by a variable power supply signal having a relatively high rms voltage (e.g., up to 150 VAC or more) and high frequency (e.g., over 2 KHz). Although, the switching system of Williams switches between loads only when the voltage of the supply phase connected by the device is substantially zero, additional circuitry is needed to perform this function and limitations on the flexibility to switch between loads result.
Furthermore, it is often desirable for an electroluminescent load to appear as if it xe2x80x9csnaps onxe2x80x9d when enabled and xe2x80x9csnaps offxe2x80x9d when disabled, generally in a time less than or equal to 50 ms. Since an electroluminescent load effectively acts as a light emitting capacitor, when a driving voltage is removed from an electroluminescent load the voltage across the load discharges relatively slowly, making the snapping off effect difficult to achieve with the above described sequential control systems.
Consequently, there is a need for a control circuit that is capable of sequentially activating a plurality of electrical (particularly electroluminescent) loads in an efficient manner, that is capable of switching a relatively high voltage and frequency power supply signal between loads, that is able to provide a desired snap off effect when disabling a load, and that is compatible with DMX controllers and signaling. It would be further advantageous if such a control circuit used only a minimal number of DMX channels to sequentially control a large number of loads so that additional DMX channels or resources are available for controlling other devices and so that the DMX control signal is refreshed at a higher rate.
The present invention relates to a control circuit suitable for sequentially driving a plurality of electrical loads, such as electroluminescent loads in any desired order. The loads may be driven one at a time or one subset at a time.
In one aspect, the control circuit is preferably compatible with the standard lighting control signal protocol DMX-512, but alleviates many of the economic and technical burdens associated with conventional one-to-one DMX switching systems. In particular, when sequencing of plurality of electrical loads, it is not necessary to fully exploit the versatility offered in conventional DMX switching systems. In addition, it is not cost effective to use an individual power supply (such as an inverter, neon transformer, DC power supply, etc.) to drive each of the loads. The present invention exploits the convenience of using a DMX interface and control protocol but only requires a minimal number of DMX channels and only one inverter power supply (or other power source depending on load) to control and power the sequencing of a large number of outputs or loads. In another aspect, the control circuit permits the switching of an electrical drive signal (e.g., an inverter output voltage) between a plurality of electroluminescent loads in a rapid, efficient, and appropriate manner including the ability to xe2x80x9csnapxe2x80x9d loads on and off, even where the voltage and/or frequency of the electrical drive signal varies. The control circuit of the present invention is also preferably implemented in a modular configuration so that sequencing applications with varying numbers of loads can be easily accommodated.
Thus, in one embodiment, the present invention provides a control circuit for sequentially driving a plurality of electrical loads (e.g., one at a time) in which a converter circuit receives a DMX compatible digital control signal and extracts a plurality of address bits from that signal. A decoder circuit receives the digital address bits and in response generates a plurality of enable signals, each corresponding to a particular electrical load. At any one time, only a subset of the load enable signals is in an active state and each other enable signal is in an inactive state. In one embodiment, only one load enable signal can be active at any one time. A relay circuit then receives the plurality of enable signals, and in response passes an electrical drive signal, such as an inverter voltage, to each electrical load that corresponds to an enable signal that is in the active state.
Where the converter circuit extracts M address bits, the decoder circuit generates N enable signals, where N and M are integers with Nxe2x89xa62M. In one preferred embodiment N=2M, e.g. M=8 and N=256. Preferably, the converter circuit extracts the plurality of address bits from data bytes for one or more DMX channels in the control signal. For example, the converter circuit may extract one address bit from a data byte for each of a plurality of DMX channels in the control signal. Alternatively, the converter circuit may extract the plurality of address bits from a data byte for a single DMX channel in the control signal (e.g., all eight channel bits). The converter circuit may comprise an address switch for specifying a DMX start channel.
The relay circuit may comprise a first plurality of relay devices, each coupled to one of the enable signals so that when that enable signal is in the active state, the electrical drive signal is coupled or passed to the corresponding electrical load. The first relay devices are preferably a solid state relay devices, but they may also be electromechanical relay device or any other type of relay devices. Especially in the case of electroluminescent loads, the relay circuit preferably also comprises a plurality of discharge circuits for rapidly discharging each electrical load when the enable signal corresponding to that load changes from the active state to the inactive state. Each discharge circuit preferably comprises a second relay device and also preferably establishes a low impedance shunt connection across the corresponding electrical load when the enable signal corresponding to that load changes from the active state to the inactive state.
The electrical drive signal may be an AC voltage signal and may have a variable frequency and/or voltage which are also controlled by other channels in the DMX control signal. In one implementation of the control circuit, the relay circuit is implemented on a plurality of boards, each board corresponding to a group of electrical loads. In another implementation, the decoder circuit and the relay circuit are implemented on a plurality of boards, each board corresponding to a group of electrical loads.
In another embodiment, the present invention provides a control circuit for sequentially driving a plurality of electroluminescent loads. The control circuit comprises a decoder circuit for receiving a digital address signal and in response generating a plurality of enable signals, each corresponding to a particular electrical load. Again, at any one time, only a subset of the load enable signals is in an active state and each other enable signal being in an inactive state. A relay circuit comprises a plurality of first relay devices each coupled to one of the plurality of enable signals as well as to the load corresponding to that enable signal. When that enable signal is in the active state, the relay device couples the electrical drive signal to the corresponding electrical load. The relay circuit also comprises a plurality of discharge circuits for rapidly discharging each electrical load when the enable signal corresponding to that load changes from the active state to the inactive state. Each discharge circuit comprises a second relay device, and both the first and second relay devices are preferably solid state relay devices.